1. Field of the Invention
This invention relates generally to magnetic recording hard disk drives (HDDs), and more particularly to a HDD that has at least one read/write head capable of accessing more than one disk surface.
2. Description of the Related Art
Magnetic recording hard disk drives (HDDs) have a stack of rigid magnetic recording disks rotated by a spindle motor, and an actuator that moves the read/write heads across the surfaces of the rotating disks, with each disk surface being accessed by an associated read/write head. The disks in the stack are in a fixed position relative to one another and are not movable axially, i.e., in a direction parallel to the axis of rotation of the spindle motor. Each read/write head is formed on an air-bearing slider attached to one end of a suspension, and each suspension is attached at its other end to a rigid arm of the actuator.
The conventional HDD can have high performance, i.e., low access time to read or write data, because all of the read/write heads are located on their associated disk surfaces and available to read or write data. However, the requirement to have a read/write head for each disk surface increases the cost of the HDD. As the need for disk storage increases, there is a desire to reduce the cost of HDDs, where cost is measured in terms of dollars per gigabyte ($/GB) of storage. A large contributor to HDD cost are the read/write heads and their associated assemblies and cabling connections to the HDD electronics. Low-cost HDDs have been proposed that have at least one read/write head that is capable of accessing more than one disk surface. In such an HDD a mechanism is required that moves the head or heads relative to the stack of disks so that the heads can be moved from one disk surface to another disk surface. As the number of disks is increased in this type of HDD, the $/GB decreases substantially while the storage capacity increases. This relationship is similar to that for magnetic tape libraries and optical disk libraries, so this type of HDD has potential application for use as a virtual tape library (VTL).
In this type of HDD where the head must be moved from one disk surface to another disk surface, there is time required to move the head or heads. During this time the disk drive cannot read or write data, so reading and writing must be temporarily halted each time the head is moved to a different disk surface. While this may not be a considerable performance impact when the HDD is used in the conventional manner, i.e., random reads and writes of relatively small files, it can pose a significant disadvantage when the HDD is used for continuous reading or writing of data, as in a VTL, or for reading or writing of large files, like multimedia files, that may be required to be stored on more than one disk surface.
What is needed is a low-cost HDD that has at least one read/write head capable of accessing more than one disk surface, but that does not require suspending the reading and writing of data when the head or heads are being moved from one disk surface to another disk surface.